Kinetics Flashcards
define rate of reaction
- how quickly a reaction happens
- the rate of change in concentration
- depends on how quickly the concentration of reactant or product changes with time
Rate of reaction equation
increase in product conc/ time taken
OR
decrease in reactant con/time taken
What unit is rate expressed in?
moldm-3s-1
What does a curved graph instead of a straight line tell us?
the gradient is not constant
How can you measure the rate of reaction on a graph?
draw a tangent to the curve at the time asked for
Why is the rate of reaction greater at the start of the reaction?
There is a greater reactant concentration
How would you measure rate of reaction if:
a. reaction produces colored precipitate
b. reaction produces gas
a. measure change in color
b. measure change in volume or mass of gas
Explain how to set up 2 experiments to measure the volume of gas produced.
- gas syringe moves outwards as gas collects
- gas collected by displacement of water from inverted burette. Gas has to have low solubility in water
Explain how to set up experiment measuring the change in mass.
- on digital balance, set beaker with cotton wool to prevent escape of liquid and solid
- but some gases are too light to show changes in mass
- needs continuous readings
kinetic molecular theory
particles in a substance move randomly because of the kinetic energy they possess
Do all particles in a substance have the same energy?
No. The random nature of movement and collisions means particles will have a range of energy values
What is the best way to measure the kinetic energy of a substance?
Take the average of the energy values of each molecule, and relate it to absolute temperature (temp measured in kelvin)
What does the Maxwell- Boltzmann distribution curve show?
Particles in a gas at a particular temperature show a range in their kinetic energy values
What is plotted on x and y axis in Maxwell-Boltzmann distribution curve?
x- kinetic energy
y- number of particles with kinetic energy
How do reactions occur?
- reactants placed together
- kinetic energy that particles possess cause them to collide with each other
- result: bonds between reactants broken, bonds form. Thus, products form
What is the collision theory?
- particles must collide
- particles must have sufficient energy
- particles must collide with correct orientation
What do many collisions lack?
Sufficient energy and correct orientation to break bonds of reactant
Activation Energy
energy required for reaction to take place
What are the factors affecting the rate of reaction?
- temperature
- concentration
- particle size
- pressure
- catalyst
Why is activation energy necessary?
- to overcome repulsion between molecules
- to break some bonds in reactants before they can react
Draw and label an endothermic graph
(look in book)
Draw and label an exothermic graph
(look in book)
Which particles can have successful collisions?
Particles that have a kinetic energy value greater than the activation energy will have successful collisions.
Do reactions with high or low activation energy proceed faster?
- high Ea reactions are slow
- low Ea reactions are faster
Explain the affect of temperature on the rate of reaction
increase in temp
- increase in average kinetic energy
- increase in collisions, moving faster
- higher proportion of molecules have activation energy, more successful collisions
+affects sufficient energy and collision frequency
Explain the affect of particle size on the rate of reaction
- decreasing particle size (increasing surface area) increases rate of reaction, i.e. powder
+affects collision frequency
Explain the affect of pressure on the rate of reaction
- increases number of collisions
+affects frequency of collisions
Explain the affect of a catalyst on the rate of reaction
- increase rate of reaction by lowering Ea, by providing an alternate pathway
- lower reaction energy by providing surface for reaction and weakening bonds
+affects collisions
Explain the affect of concentration on the rate of reaction
-increase concentration: increases rate of reaction
+affects collision frequency and successful collisions
How do catalysts lower reactivation energy?
- Providing surface for reaction
- Weakening bonds of reactants
What is the effect of temperature on a Maxwell- Boltzman distribution graph?
- at higher temperature- more particles have kinetic energy value greater than Ea
- at low temperature- less particles have kinetic energy value greater than Ea
Define and state the advantage and disadvantage to heterogenous catalysts.
- catalysts in different state than reactant
- easy to remove
- doesn’t spread easily
Define and state the advantage and disadvantage to homogenous catalysts.
- same state as reactant
- mixes easily
- difficult to remove`
State the techniques for measuring the rates of reaction. (6 ways)
Measuring
- change in volume of gas
- change in mass
- change in transmission of light: colorimetry/ spectrophometry
- change in concentration measured by titration
- change in concentration measured using conductivity
- non-continuous methods of detecting change during a reaction - clock reactions
Describe how to measure the rates of reaction through the change in transmission of light.
- indicator added sometimes to generate color
- colorimeter or spectrometer passes light of specific wavelength through solution
- measures intensity of light transmitted by reaction components
- substances with higher concentration absorb more light, therefore transmitting less
- photocell generates electric current according to light transmitted
- continuous readings
- determine rate of reaction by measuring decrease in absorbance
Describe how to measure the rate of reaction through the change in concentration measured using titration.
- measure concentration of one of reactants or products by titrating it against known standard
- no continous readings
- identify: reactant and product includes water
Describe how to measure the rate of reaction through the change in concentration measured using electricity
- electrical conductivity or a solution depends on total concentration of its ions and charges
- measured using conductivity meter
- measure difference in concentration of ions between reactants and products
- decrease in concentration of ions- decrease in electrical conductivity
- identify: metals, Br, Al
Describe how to measure the rate of reaction through the non-continuous methods of detecting change during a reaction: clock reactions
- measure time it takes for reaction to reach observable fixed point
- enact same reaction under different conditions, find different timings, and judge different rates of reaction
True or false: are rate and time indirectly proportional?
True- rate= 1/time
